1. Field of the Invention
This invention is related to improvements in the metal foils employed in food packages which are used to heat or cool foods. More particularly the invention relates to improvements in the coatings used and their method of application to metal foil pouch stock which is converted into foil packages used to heat foods in the ordinary domestic bread toaster.
2. Description of the Prior Art
Recent developments in the food packaging and servicing industry have led to the increased interest in heating pre-cooked foods in a conventional bread toaster used in the home. It has been known to provide pre-cooked bacon strips in a sealed metal foil pouch which was adapted to be inserted into a toaster for heating to complete cooking. Such pouches and foil pouch stock are disclosed in one or more of the following U.S. Pat. Nos. 3,469,998; 3,554,700; 2,912,336; 3,615,711 and 3,185,372. The potentially attractive market for pre-cooked foods capable of being heated to completion in a toaster has increased interest in the possibility of providing a wide range of food products which might be pre-cooked for subsequent heating in an ordinary bread toaster.
Bacon strips can be easily prepared in a toaster because of the relatively small cross section of the individual bacon strips. Although problems are encountered regarding grease collection and uniform heating throughout the foil pouch, pouches which are technically satisfactory for the bacon strip application have been developed. It is when one elects to heat foods with larger cross sections and/or densities such as hamburger patties that the current metal foil pouch stock tends to fail, both from the standpoint of non-uniform heating, and consequently non-uniform cooking, of the food product within the pouch and the thermal decomposition of the exterior and interior coatings on the foil.
Compounding the above shortcomings of the current metal foil pouch is the fact that larger, denser food products require longer times in the toaster environment in order to heat to completion. Whereas bacon strips may be prepared in a toaster in 90 seconds, the time to heat a hamburger patty to completion will approach 5 minutes. This added time in the toaster materially contributes to the decomposition of known, coated metal foils.
Still another problem has been experienced when attemtping to extend the utility of existing metal foil pouch stock to the more lengthy times at the temperature required to complete the cooking process. Many of today's household toasters employ a heat sensor to control the time of product dwell in the toaster rather than a timer or thermocouple in the well of the toaster. The heat sensor measures the quantity of infrared radiation being absorbed or reflected from the object being heated and discharges the object from the toaster heating well when an appropriate temperature is obtained. Toasters employing such a heat sensing device have been difficult to use to heat pre-cooked foods when the food product assumes the size and density of products such as a hamburger patty, because there is a lack of uniform heating throughout the pouch while in the toaster. The lack of uniform cooking stems from the fact that the food product within the metal foil pouch is adjacent to both an unprinted lower portion of the pouch and a printed upper portion of the pouch. The printed section of the pouch is characterized by a different heat reflectivity than the unprinted regions of the pouch consequently resulting in variations in heat absorption and non-uniform cooking. Printed matter is generally necessary or desirable in order to provide the consumer with readily available heating instructions and to communicate the procedure to be followed when inserting and removing the pouch from the toaster.
Standard printed characters may be provided on the upper portions of the metal foil pouch stock by providing a top coat of one color over a base coat of a different color on the foil and permitting the base coat to show through in the form of printed characters. The size, quality and quantity of these printed characters in turn is all important because their legibility may be affected by the application of the top coat. This is particularly true when the characters are relatively small because the fluid coating migrates uncontrollably to effectively blurr the characters. In practice, the size and frequency of the printed characters controls the weight of top coat which can be applied without adversely affecting the legibility of the printing. When the top coat is of uniform weight and thickness, the unprinted portions of the foil do not receive enough coating material to effectively control the uniformity of heat input, into the food product.
It has been known that the rate of heat absorption of metal foil may be varied and consequently controlled by using different colored coatings (U.S. Pat. No. 3,079,912) and by applying coatings to selected regions of the foil (U.S. Pat. No. 3,079,913). Further, U.S. Pat. No. 3,469,998 teaches the technique of applying different colored coatings and overcoatings to different pouch foil sections thereby providing for more uniform heat distributions throughout. These and other prior art teachings do not, however, overcome the problem of retaining the uniformity of heat absorption while at the same time providing for legible printing on the foil.
There remains, therefore, a need for a method of applying a top exterior coating to the base coated metal foil to establish distinct variations in coating weight for different portions of the foil pouch stock to provide for legible, printed instructions and uniform heating of the enclosed food. The need is particularly acute with respect to a toaster foil pouch suitable for heating foods in a domestic bread toaster for longer times than heretofore known without an adverse effect on the pouch or its attendant coatings.